This research proposal concerns the enzymes which are involved in the activation of the bile acids cholate, chenodeoxycholate and deoxycholate with coenzyme A and then their subsequent conjugation with glycine or taurine. The enzymes are (for cholate) cholate:CoA ligase (I), glycine:cholyltransferase (II) and taurine:cholyltransferase (III). This proposal is aimed at a characterization of the properties of the cholate and deoxycholate and chenodeoxycholate enzymes and their functional dependence on the lipid environment of the microsomal membrane to which they are reputed to be bound. The first step will be to carry out for the first time a complete kinetic analysis of all three reactions for each bile acid, using specially developed assay techniques. The hypothesis that reactions (II) and (III) are catalyzed by separate enzymes is to be determined using alternate product and alternate substrate inhibition studies. Further, the question of whether any of the enzymes are common to both cholate and deoxycholate conjugation will be investigated. The basis for the dramatic changes in the ratio of glycine to taurine conjugated bile acids accompanying development and certain diseases will be analyzed by a comparative study of the kinetic parameters of enzymes (II) and (III). Further, animals which fail to make either glycine or taurine conjugates will be examined to determine if there is an enzymological basis for the deficiency.